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What may be the oldest-known Earth rock has turned up in a surprising place: the moon. A 2-centimeter chip embedded in a larger rock collected by Apollo astronauts is actually a 4-billion-year-old fragment of our own planet, scientists say.
“It’s a very provocative conclusion but it could be right,” says Munir Humayun, a cosmochemist at Florida State University in Tallahassee. The finding “helps paint a better picture of early Earth and the bombardment that modified our planet during the dawn of life,” says David Kring, a lunar geologist at the Lunar and Planetary Institute in Houston, Texas, and lead author of a study published on 24 January in Earth and Planetary Science Letters.
Rock - Kring - Impact - Earth - Way
Sometime after the rock formed, Kring says, an asteroid impact blasted it from Earth. It found its way to the moon, which was three times closer to Earth than it is today. The fragment was later engulfed in a lunar breccia, a motley type of rock. Finally, Apollo 14 astronauts returned it to Earth in 1971. Although geologists have found meteorites on Earth that came from the moon, Mars, and asteroids, “This is the first time a rock from the moon has been interpreted as a terrestrial meteorite,” says Elizabeth Bell, a geochemist at the University of California, Los Angeles, who was not part of the study.
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Several years ago, a team led by Kring detected fragments of asteroids in similar moon rocks, so looking for pieces of Earth was a logical next step.
Trace - Elements - Rock - Minerals - Mix
Trace elements in the rock’s minerals, which are a granitelike mix of quartz, feldspar, and zircon crystals, provided clues to its origin. By measuring uranium and its decay products in the zircons, the team dated the formation of the rock, while titanium levels...
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